(1) Field of the Invention
This invention relates to a semiconductor device-encapsulating epoxy resin composition which exhibits improved moisture-resistance after it is subjected to a thermal cycle, and which has low water absorption.
(2) Description of the Related Art
Epoxy resins have good heat resistance, moisture resistance and electrical characteristics, and various characteristics can be obtained by modifying the receipes thereof. Accordingly, epoxy resins are used as for paints, adhesives and industrial materials.
As methods of encapsulating electronic circuit parts such as semiconductor devices, known methods include a hermetic encapsulating method using metals or ceramics, and a resin encapsulating method using a phenol resin, a silicone resin, an epoxy resin or the like, but from the economical viewpoint, productivity and the balance among the physical properties, the resin encapsulating method using an epoxy resin is mainly adopted.
In the field of semiconductor integrated circuits, techniques of enhancing the integration degree have recently been developed, and the size of semiconductor elements is becoming large and the wirings in the elements are becoming fine. When such conductor elements are encapsulated with an epoxy resin, a strain occurs due to shrinkage caused by curing or thermal shrinkage caused by cooling. This strain leads to a shift of the aluminum wirings, breakage of the bonding wires and cracking in the semiconductor elements or the resin encapsulating the semiconductor device, with reduction in reliability.
As a curing agent for an epoxy resin, a phenolic novolak resin and a cresol-novolak resin have heretofore been used, but these novolak resins lave a problem such that the cured epoxy resin exhibits poor moisture resistance after it is subjected to a thermal cycle, and has a large water absorption.
It has been proposed to use 4,4'-dihydroxy-3,3',5,5'-tetramethylbiphenyl as the curing agent for an epoxy resin (see a preprint of the I.E.E.E. 1990 Conference, page 625). In this preprint, the solder cracking resistance of the epoxy encapsulating resin cured by using 4,4'-dihydroxy-3,3',5,5'-tetramethylbiphenyl is discussed. It is rather doubtful, however, whether this curing agent enhances the solder cracking resistance, and the reactivity of the curing agent is poor and the cured epoxy resin composition has a low glass transition temperature and a poor moisture resistance. Therefore, the cured epoxy resin composition has poor reliability and practicality.